The ultimate goal of this revised proposal is to understand the molecular pathogenesis of human acute myeloid leukemia (AML), using the AML-1/ETO chimeric transcription factor as a model system. The t(8;21) translocation, seen in the M2 subtype of AML, invariably generates AML-1/ETO fusion transcript which results in the expression of a chimeric transcription factor protein. The applicant has demonstrated that the normal AML-1B protein, but not the normal AML-1A protein, can transactivate the human GM-CSF promoter via a TGTGGT sequence located between bp-57 and -52 and can transactivate the human IL-3 promoter via a similar sequence. The AML-1/ETO protein can inhibit transcription from these promoters and can act as a dominant negative regulator of the GM-CSF promoter. The Specific Aims of this proposal are to 1) define the basis for the differential effects of the normal AML-1A and AML-1B proteins and the AML- 1/ETO fusion protein on a) the activity of the human GM-CSF and IL-3 promoters and b) the regulation of bcl-2 expression in AML cell lines and the prevention of apoptosis; 2) identify cellular partners capable of interacting with AML- 1/ETO using a) the yeast two-hybrid system and b) bacterially or mammalian cell expressed AML-1/ETO fusion proteins; and 3) determine the effects of introducing the AML-1/ETO fusion gene on the proliferation and differentiation of normal hematopoietic progenitor cells and acute myeloid leukemia cell lines. These studies will define the interactions of AML-1/ETO with its DNA recognition sequences and with other cellular proteins. This study will also demonstrate whether AML-1/ETO generates anti-apoptotic signals and whether it has transforming activity by itself. Understanding how the AML-1/ETO fusion protein alters the cells' proliferation and differentiation program may provide insights into the pathogenesis of AML.